The present invention relates generally to improvements in waste treatment. More particularly, this invention relates to substantially closed looped waste treatment and water recycling toilet systems.
Waste treatment and water recycling toilet systems to which the present invention relates are generally shown in U.S. Pat. No. 3,950,249 issued Apr. 13, 1976 and U.S. Pat. No. 4,210,528, issued Jul. 1, 1980. U.S. Pat. No. 4,904,387, issued Feb. 27, 1990, which is hereby incorporated by reference, discloses a closed loop waste treatment and water recycling toilet system. The above patents are all commonly assigned to the assignee of the present application.
Municipal-type sewage treatment systems have lowered the organic compound and nitrogen concentration in the treated sewage by biologically treating the sewage under anoxic conditions followed by subsequent biological treatment under aerobic conditions. This sequence is advantageous because the bacteria in the anoxic reactor utilize organics found in the sewage to accomplish the breakdown of nitrates. Thus, a limited amount or no supplemental organic source needs to be added into the system. Such a flow through system, however, does requires the removal of sludge, creating the problem of sludge transport and disposal. Additionally, some of the nitrates produced during the treatment process flow out of the system and are not fully removed by the system.
Closed loop systems which recycle effluent for toilet-flush use have been advantageous in waste treatment since little or no external water supply is needed, thereby minimizing the unnecessary use of potable flush water. Difficulties have arisen, however, in the biological treatment processes of these systems. As a result of these deficiencies, inadequate treatment of waste often results in the production of obnoxious odors and colors in the flush water along with a rapid accumulation of biological solids in the system.
The closed loop system disclosed in U.S. Pat. No. 4,210,528 provides a system having effective management of nitrogen so that the system can be made of a reasonable size while avoiding undesirable odors, color and the buildup of solids. U.S. Pat. No. 4,904,387 discloses a system in which the management of the nitrates and nitrogen in the system is improved to increase treatment efficiency.
In closed loop systems where the majority of the processed waste water will be recycled and subsequently returned back to the system and where the remaining portion will be discharged, generally to ground water either through subsurface leaching or surface irrigation, it is desirable to remove nitrates from the discharged water. Discharge regulations sometimes require a nitrate-nitrogen concentration level of less than ten milligrams per liter (10 mg/l).
It is therefore an object of the present invention to provide for the enhanced treatment of discharge water in a waste water treatment and recycling system. The treatment decreases nitrate concentrations in the discharge water to levels below drinking water standards.
Another object of the present invention is to provide a nitrate removal system in which a nitrate removal medium used in the secondary removal step can be regenerated within the system without harm to the system or without detriment to the system's efficiency.
In accomplishing the above objects, the present invention provides for nitrate-nitrogen removal from water which is to be discharged from a substantially closed loop water recycling toilet system. The water recycling toilet system of the present invention includes a waste delivery system, a trap, a sump chamber, an anoxic chamber or reactor, an aerobic digestion chamber, a filter, absorption and disinfection systems, along with a water return and nitrate removal stations.
The delivery system, as illustrated, includes a single flush-type toilet. It should be understood, however, that it could include a plurality of toilets or a number of toilets and a number of urinals. As used herein, the term "toilet" is inclusive of all of the above. In addition to delivering toilet waste, the delivery system receives all the waste water from the facility in which it is installed, including waste water from sinks, lavatories, dishwashers, showers and the like. The delivery system includes a means for drawing flush water to the toilet from the water return system and means for delivering the waste and flush water to the trap and the sump.
From the sump, the mixture of waste and flush water is transferred into the anoxic reactor which contains a bacteria laden sludge. The anoxic reactor also contains an agitator means which periodically mixes the contents of the reactor to enhance de-nitrification of oxidized nitrogen compounds, such as nitrates, in the mixture.
While the process of biological de-nitrification is complex and not yet fully understood, it is generally accepted that facultative bacteria, which exists in the sludge, satisfies its metabolic requirements preferentially through the dissolved oxygen found in the waste liquid. However, if the supply of dissolved oxygen is sufficiently low, anoxic conditions will exist and, under these conditions, the bacteria will reduce oxygen containing compounds, such as nitrates or other oxidized nitrogen compounds. The anoxic reactor in this invention is maintained under these conditions.
Since the bacteria in the anoxic reactor utilizes toilet waste as the source of organics needed to effect the breakdown of nitrates and other oxidized nitrogen compounds, the amount of organic waste in the reactor is substantially lowered and bicarbonates are produced. The nitrogen gas which is also produced in the reactor is vented from the system.
Liquid from the anoxic reactor has a high concentration of bicarbonates and ammonium compounds and a low concentration of nitrates. It can therefore be seen that the anoxic reactor is not located in the system to accomplish the breakdown of nitrogenous compounds, such as ammonia, but rather to remove nitrates from the flush water and a substantial quantity of organic material from the toilet waste. The bicarbonates produced in the anoxic reactor are themselves necessary for the complete oxidation of ammonium compounds in subsequent processes of the toilet waste treatment system.
Liquid from the anoxic reactor is transferred to the aerobic digestion chamber. The aerobic digestion chamber contains biologically active solids and an aeration means which is operated to provide a sufficient amount of oxygen to effect both the oxidation of the organic compounds and the nitrification of nitrogenous compounds. Although biological nitrification is also not yet fully understood, it has been found that under sufficient oxygen conditions, the nitrifying bacteria in the biologically active solids are able to oxidize the ammonium compounds and convert the compounds into nitrates. The aerobic digestion chamber is maintained under these conditions so that the bacteria will utilize the bicarbonates found in the mixed liquid as the necessary carbon source for accomplishing the desired nitrification. The fluid from the aerobic digestion chamber is therefore low in ammonium and carbonatious compounds, but is high in nitrates.
As used herein, the expression "biologically active solids" includes bacteria in both a suspended growth form and an attached growth form. In a suspended growth reactor, the bacteria is in suspension in the material commonly called "activated sludge" while, in an attached growth reactor, the bacteria is attached to solid bodies within the reactor. While the invention is particularly described with respect to the use of activated sludge in the aerobic digestion chamber, it should be understood that it is within the purview of this invention to use bacteria in the attached form.
Liquid is removed from the aerobic digestion chamber and passed, under pressure, to filters which remove suspended solids, colloidal matter, and large amounts of bacteria from the liquid. The suspended solids, colloidal matter and bacteria are then transferred back to the aerobic digestion chamber.
From the filter, filtrate is transferred to an absorption station which includes a bed of activated carbon. The internal pore structure and the affinity of the activated carbon for organic matter removes undesirable colors and odors from the filtrate. The filtered liquid is then disinfected and transferred to a water storage tank from which, on demand, it is delivered to the toilet as flush water completing the system's cycle.
Processed water in excess of the flush water requirements is treated in a nitrate removal system before being discharged. Since more water is being processed then is needed for flush water requirements, the supplemental, de-nitrified water is discharged from the system.
Due to the arrangement of present invention, nitrates produced in the aerobic digestion chamber are present throughout the filtering, absorption, disinfecting, water return and delivery systems. The presence of nitrates in the liquid passing through the filtering and absorption systems prevents the reduction of sulfates which may also be present in the liquid. The reduction of sulfates would otherwise cause the production of hydrogen sulfide which has a readily recognizable obnoxious odor. Nitrates are still present in the flush water as it is delivered with toilet waste into the anoxic chamber. This induces greater biological destruction of organic waste and increased production of bicarbonates for use in the aerobic digestion chamber. The management of nitrates in the present system therefore prevents production of hydrogen sulfide or other obnoxious odors, provides for efficient biological treatment of toilet water and a corresponding reduction in the size requirements for the aerobic digestion chamber.
The present invention also provides for indefinite retention of sludge solids. This ensures sufficient microorganism age to accomplish the desired results in the biological treatment process. In the system of this invention, the amount of biologically active solids in the aerobic chamber and the amount of organic material supplied from the anoxic reactor are balanced so that minimum sludge accumulation and maximum nitrification rates are achieved in the aerobic chamber. The elimination of excess sludge production, and the corresponding need for its disposal, reduces the potential pollution of external and subterrainean water supplies. Also, the recycling and reuse of water prevents the further unnecessary usage and pollution of water supplies.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with accompanying drawings.